was he talking about the back side of the tank? kinda the only way be nice and easy to change the background.
but yeah i have herd of people using it on pipes and decorations. but when you have alot of water, and little product that could be poisonous it would get watered down. when your spraying an entire backing and bottom of tank its alot of square footage of material that could be leeching out toxins into the water.
and thats the real concern.